When I turn the hester on only cold air blows out. Is this something that I could fix without taking it to the dealer. I have a 97 GMC Silverado.

 

If you have a temp gage on your dash check to see if the temp is normal ... could be a thermostat stuck open.
Could be the damper door to the heater core may be stuck.

 

Warm the truck up and put the heat on high see if both lines going to the heater core are hot. if so you have heat going thru the core
I had 1 hot 1 and one cold one.

I replaced my thermostat and took a garden hose and blew out the lines that wnet to the heater core. It's worked fin ever since on both my chevys.

On the chevy blazer forum http://www.blazerforum.com/forumid_5...smode_1/tt.htm their must be at least 20 posts regarding heater problems. I have a 98 k1500 and a 98 blazer and both trucks share a lot of the same issues such as trannys going at the same time, no heat and only heat going thru defrost, cold air thru other vents.. My blazer is now experiencing an anti freeze smell and their are good posts to a remedy as well on this forum.